High-frequency transformer



Aug. 'i3, 1929. H. F. ELLIOTT 1,724,399

' HIGH FREQUENCY TRANS-FORMER Filed Sept. 17, 1927 2 Sheets-Sheet l INVENToR #Jam/d F. E//fb/ HIS ATTORNEY Aug. 13, 1929. H. F. ELLIOTT HIGH FREQUENCY TRANSFORMER Filed Sept. 17, 1927 Sheets-Sheet 2 PIE- 7.

PIE- E- Patented Aug. 13, 1929.

UNITED STATES PATENT OFFICE.

HAROLD F. ELLIOTT, 0F PALO ALTO, CALIFORNIA, ASSIGNOR. BY DIRECT AND MESNE ASSIGNMENTS, TO VICTOR TALKING MACHINE COMPANY, OF CAMDEN, NEW JER- SEY, A CORPORATION OF NEW JERSEY.

HIGH-FREQUENCY TRANSFORMER.

Application filed September 17, 1927. Serial No. 220,151.

This invention relates to radio signaling systems, and especially to radio frequency transformers utilized in connection therewith.

In radio receivers, it is now quite common to utilize one or more radio frequency amplifier stages, whereby the signaling impulses are first amplified, as by thermionic amplifiers, before detection. Radio frequency coils or transformers are used to pass the impulses from one stage to the next stage.

It is one of the objects of my invention to improve in general, this type of coil or transformer.

When electronic emission devices are utilized as the amplifiers, certain complications occur which will now be discussed. Such amplifiers usually include a source of electrons, such as a filament heated by the passage of electric current through it, and a plate or anode to which the electrons are attracted. The plate is kept at a potential positive with respect to the filament as by a battery or the like connected between the electrodes. The space current formed by the electrons can be controlled by a third electrode or grid placed in the tube, by controlling the potential difference between the grid and the filament. It has been found that small changes in this potential difference cause much larger corresponding changes in the space current; and thus an amplifying effect is produced, The variations in the space current are caused to affeet the current fiow in the output circuit connecting the filament and plate, and this current in turn can serve to impress varying potentials upon a grid of a succeeding amplifier.

It has been found that such an amplifier has a tendency to become unstable, due to the parasitic capacity effect between the grid and plate, and the conditions of the circuits connected to these electrodes. For overcoming this instability, a neutralizing circuit can be used; and such a neutralizing circuit involves the addition of a third winding on the coupling transformer, either as a primary or as a secondary.

It is another object of my invention to provide a novel and compact transformer in which such a winding cany be easily ineluded, y

Such a transformer is described and claimed in a prior application filed March l1, 1927, in my name, having Serial No. 174,475, and entitled System of neutralization. My present application is a continuation in part of said prior application.

In order to secure the best results with such amplifier' systems, it is essential to reduce as much as possible, all sources of inefficiency, as for example, the energy losses in the dielectric material between conductors or windings on the transformer. IVith the aid'of my invent-ion, such dielectric losses are reduced to a low value.

It is also well-known that in order to secure undistorted and stable amplification, the radio frequency circuits should be shielded from one another and from stray effects. It is another object of my invention to produce a compact transformer that can be arranged in a shield without any difficulty.

My invention possesses many other advantages, and has other objects which may be made more easily apparent from a. consideration of one embodiment of my invention. For this purpose I have shown a form in the drawings accompanying and forming part of the present specification. I shall now proceed to describe this form in detail, which illustrates the general principles of my invention; but it is to be understood that this detailed description is not to be taken in a limiting sense, since the scope of my invention is best defined by the appended claims.

Referring to the drawings:

Figure 1 is a sectional view of a transformer embodying my invention and shown as supported on a frame;

Fig. 2 is a front elevation of one of the transformer frames;

Fig. 3 is a sectional view thereof;

Fig. 4c is a plan view showing a transformer disposed in a shield;

Figs. 5 and 6 are detailed front and side views of one of the parts making up the transformer structure;

Figs. 7 and 8 are diagrammatic views illustrating the mode of wiring the transformer; and

F ig. 9 is a wiring diagram illustrating one way in which the transformer can be used.

In Fig. 9 I show a radio frequency thermionie amplifier ,11 t0 WhQ/h ,radio fre-.-

quencyl impulses are passed, and which passes the amplified impulses to further amplifiers and detector, indicated by rectangle 12. The impulses to be amplified are shown as first passed to a primary winding 13 of a transformer 14, by the aid of the incoming leads 15, 16, which can connect to any desired form of pick-up system. A secondary coil 17 connects at its oppositeends respectively to the control electrode or grid 13, and to the electron emitting electrode or filament 19, as by the aid of ground connections 2() and 21. This filament shown as heated by an adjustable current from battery 22. The output circuitincludes plate or anode 23, a primary coil 24, source of positive potential 25, and filament 19.

ln order to neutralize the parasitic capacity coupling between grid 13 and plate 23, a neutralizing circuit can be used, such for example as that connecting plate 23 and ground 20, and including the neutralizing condenser 26 and a coil 27 closely coupled to coil 17. If coil 27 has the same inductance as coil 17, and if condenser 23 has vthe saine value as the parasitic capacity, then it can be shown that by proper connection of coil 27, the disturbing electromotive forces produced in coil 17 due to the parasitic coupling aresubstantially entirely neutralized by the electronic-tive forces induced in it by coil 27; The theory of such neutralizat-ion is now well-known, and needs no further elucidation.

ln order to tune the system to a definite.

Y Furthermore, a metallic shield 29 is indicated as encompassing the transformer 14 and condenser 28. y

The amplified impulses passed to primary 24 are in turn passed to a Vsucceeding stage that can be entirely similar to the one just described. Thus secondary coil 30 and neutralizing coil 31 are shown as coupled to coil 24, and are bridged by variable condenser 32. These parts correspond to parts 17, 27 and 23 of the firststage, and they can be used to affect the succeeding stages represented by rectangle 12. As many stages can be thus -cascaded as desired. Ultimately, a detector is utilized, and if desired, one or more stages of audio frequency amplifiers. Finally the amplified and detected impulses.

are passed to a translating device such phones 33. A shield 34 is also shown, en-

coinpassing the transformer and condenser 32.

. i e tra iza ion .iu is essenln this type of n uL l t L tial to couple closely the secondaries 17 and 27, as well as secondaries 30 and 31; and in fact in such a way that the leakage inductance of both coils be small enough to provide a very high natural period determined by this leakage andthe disturbed capacity of the system. Especially should this period be higher than the natural period of the output circuit, determined by its distributed capacity and leakage inductance. lilith the aid of my invention, the close coupling` of the two windings 17 and 27, or of 30 and 31 can be very easily accomplished, as will be evident from the following` description of the transformer details.

The transformer struc-ture 14 is shown in detail in F 1 to 8. It is shown as supported on a metallic frame 35. There a right and left support 36 and 37 made from insulation,l such as molded bakelite. The left support 37 is shown in detail in Figs, 2 and 3, and since both supports arc quite similar, the description of one of them will be sufhcient to serve as a. description of both.

Each support has a base portion 38, adapted to be fastened to the frame as by screw 39. `It further has a pair of hollow lugs 40 passing` through apertures in frame 35. These lugs serve a dual purpose: to position the supports properly on frame 35, as well as to permit connections to pass from the transformer 14 through frame 35 and below it. Each support` furthermore has an upright thin body 41 which is 4provided with a flange 42 for lendingrigidity to the structure. It also has .a circular flange 43 that serves as a support for a winding, whenthe two supported are fastn ened together.

rit the center of the support, there is a boss 44, provided with an aperture 45 whereby a bolt 46 can be passed through both sup-V ports for holding them together. The bosses 44 are held spaced apart by a series of circular projections 47 spaced annularly of boss 44, and having their centers at about the periphery of the boss. `Varies or ribs 48 connect the boss with flange 43. Furthermore, flange 49 is provided around the bolt aperture 45 to enable the transformer to be held in a chuck for Winding.

With the two supports 36 and 37 fastened together as shown in Fig. 1, the flanges 43 are separated by a considerable distance; and this space. between the flanges can be further split up into two parts by a disc 50 shown in detail in lfigs. 5 and 6. This disc is made from insulation material and is cut away as shown at 51 to provide as little` dielectric as possible. lt too has an aperture 52 for the passage of bolt 46 and is firmly clamped between bosses 44. rlhe projections 47 enter between the spokes 53 of the disc. Y

The two secondaries 17 and 27 can be wound in pancake form on opposite sides of disc 50, and between it and the supports 36 and 37. The spokes 53 and ribs 48 serve to maintain these coils in proper flat form. The primary winding 13 can be disposed over the flanges 43, but separated from them by a few layers of insulation `54, such as varnishcd cambric. It is seen that as much dielectric material is removed from the field of the coils as possible, to reduce the dielectric loss, While yet maintaining a. rigid structure.

For ordinary broadcast reception, coil 13 can be Wound With about forty-two turns, and each of the coils 17, 27 with about fortyfive turns. The` size of the Wires is exaggerated in the drawings, `Whereby the turns appear to be less in number than these values.

In Fig. 4 I show the arrangement of the transformer 14 and condenser 28 in its shield 29, which is shown as oval in forni. The condenser 28 is indicated as one having a pair of electrodes pivoted for movement about spaced axes and moved by operation of links 55, which extend through an opening in shield 29.

In order to explain the mode of Wiring the transformer, the diagrams of Figs. 7 and 8 are included. Fig. 7 is a View taken from the left of Fig. 1; and Fig. 8 is a vieu7 taken from the right thereof. In Fig. 7, coil 27 is shown as having its inner terminal brought out through aperture 56 to the outside of support 36. The lead 57 is then, for support, looped in and out of apertures 58 and 59, and is finally soldered or otherwise connected to a soldering lug 60 that is partly embedded in support 36. From this lug extends Wire 61 through one of the lugs 40 for connecting to the neutralizing condenser 26. To the lug 60 is also connected one terminal of condenser 28, as indicated by connection 62 (Fig. 4).

The outer terminal of coil 27 passes to the outside of support 36 by Way of aperture 63, and a lead 64 connects it to a ground connection. The other secondary 17 is Wound in a direction opposite that of coil 27; its inner terminal extends through aperture 65 in support 37, and is soldered to a soldering lug 66 carried by said support. Connection 67 extends from lug 66 and through the boss 40 to the grid 18. The outer termina] of coil 17 extends through aperture 68 in support 36 to connect to the common grounded center lead 64.

The connections for primary coil 13 can be best explained by the aid of Fig. 8. The terminals of this coil extend through apertures 69 and 70 respectively, in support 37 and thence they proceed through the apertured boss 40, to the preceding stage of am lication.

f course, coils 24, 30 and 31 for the next stage, can be similarly supported. and conneeted; and all further stages can be equivalently constructed.

It is to be noted that the outer terminals of coils 17 and 27 are grounded; this serves to produce a grounded electrostatic shield between the primary and secondary coils. Furthermore, due to this feature, and since the primary 13 is symmetrical with respect to the secondaries, which are themselves symmetrical both electrically and mechanically, there is very little capacity coupling between primary 13 and either of the other coils 17 and 27. This is of the highest importance, for if there were any substantial coupling, there would be a path formed for feed-back energy between the detector output back through all the preceding stages to the first stage, and this would result in material regeneration and instability.

The advantages therefore, of this design involve a definite relative arrangement of the coils to ensure close coupling, eliminattion of material feed back, and of stray capacity and leakage inductance. All these are essential for stability; and the syrnmetrical arrangement also ensures that the neutralization will be effective for the entire range of the system.

I claim:

1. A radio frequency transformer including a support made from insulation material, a plurality of coils supported therein, said support having a plurality of hollow lugs arranged to extend through a Wall, and connections for the coils passing through said lugs.

2. In a radio frequency transformer, a pair of supports of insulation material, each of said supports having a flange, means for fastening the supports together so that the flanges are coaxial but spaced apart, each of said supports also having a series of radial ribs extending between the flange and the common axis of the Hanges, a pancake coil structure disposed between the supports and supported by said ribs, and a coil Wound on the flanges.

3. In a radio fi'equency transformer, a pair of closely spaced equal pancake coils, a ground connection to the outer terminal of each of said coils, and a cylindrical coil coaxial with the pancake coils and symmetrically placed thereover.

4. In a. radio frequency coil structure, a pair of pancake coils, and means for supporting said coils close together and for reducing the dielectric loss, comprising insulation supports having spaced radial members of insulation material, one of said )Jupports being interposed between the coils, and the others respectively on the outside surfaces of the coils.

5. In a radio frequency transformer, a pair of insulation supports, each having a circular boss, as Well as a series of projections extending beyond the boss and arranged to be in engagement when the supports are fastened together, a spoked dise i of insulation material held `between the bosses, pancake coils disposed respectively between each of the supports and the disc, and a cylindrical coil disposed over the'pancake coils and supported on said supports. 6. A coil support for high frequency coils, comprising a pair of flanged supports made from insulation material, means, for fastening said supports together, each of said supports 4having a boss, said bosses being concentric when the supports are fastened together, and coaxial with the fianges, each of said supports also having a face that is opposed to the face on the other support when the supports are fastened together', and a disc clamped between the bosses and defining a pair of narrow spaces between it and the flanged supports.

. 7. The combination as set forth in claim 6, with the limita-tion that the supports and the disc are soy formed that'only a small portion of the insulation material of the disc and supports face each other.

8. The combination as set forth in claim 6, with the limitation that the disc is cut away to form a spoked disc, and the supmy hand.

HAROLD F. ELLIOTT. 

